It is known to ship, for example, produce in insulated freight containers to protect it thermally during transport. The contents of the container can frequently, however, sweat or generate liquid that collects on the floor of the container. This liquid cannot be allowed to pool as it will lead to mildew and rot problems.
Accordingly it is known from European 92 104023 to provide the floor of the container with a drain constituted as a tubular guide forming a passage that extends through an upwardly open valve seat. A floatable, that is lighter than water, ball is captured in the guide and can sit on the seat, normally blocking flow through it in either direction. When, however, water collects in the guide the ball floats up to unblock the passage and allow the water to drain out. Once the water is drained out the ball reseats and prevents, for example, cold air from blowing back in through the passage and freezing the contents of the freight container.
A problem with such a drain is that the base of the container is frequently exposed to considerable wetness. In fact on ship board it is possible in bad weather for the floor of the container to be actually submerged somewhat in sea water. In this case the ball floats up and water can enter the container, ruining the freight therein.
It has been suggested to provide a relatively tall structure with a rubber sleeve that closes to prevent such reentry, but this system has not proven itself effective in use. The sleeve is often damaged and/or torn off by handling of the freight container. In addition the structure is relatively tall and bulky so that it cannot readily be built, for example, into a standard-size cargo transcontainer.